Hillock-free aluminum layer and method of forming the same

ABSTRACT

A hillock-free conductive layer comprising at least two aluminum (Al) layers formed on a substrate, wherein said at least two Al layers comprise a barrier Al layer formed on the substrate, and a pure Al layer formed on the barrier Al layer. The barrier Al layer could be an aluminum nitride (AlNx) layer, an aluminum oxide (AlOx) layer, an aluminum oxide-nitride (AlOxNy) layer, or an Al—Nd alloy layer. Also, the pure Al layer is physically thicker than the barrier Al layer, for effectively inhibiting the occurrence of hillocks and the like.

This application claims the benefit of Taiwan applications Serial No.092119085, filed Jul. 11, 2003, and Serial No. 093103832, filed Feb. 17,2004, the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to an aluminum (Al) conductive layer,and more particularly to a hillock-free Al layer and a method of formingthe same.

2. Description of the Related Art

As the semiconductor manufacturing of an integrated circuit (IC) withlarger scale is required, a substrate may be insufficient to provide anenough area for forming required interconnects for the IC. In order tomeet the requirement of the formation of increased numbers ofinterconnects due to the reduction of metal oxide semiconductors (MOSs)of the IC in sizes, two or more levels of metal layers for interconnectshave become a necessary technology adopted in the manufacturing of manyICs. Particularly, for some integrated circuits with sophisticatedfunctions such as microprocessors, four or five levels of metal layersare required to implement interconnections of the components of theintegrated circuits. On the other hand, in the manufacturing of athin-film transistor liquid crystal display (TFT-LCD) panel, the metalfilms are employed as electrodes and interconnects, which are alsoformed in a structure with multiple layers of metal films.

In a structure with multiple layers of metal films, there are insulatinglayers, such as dielectrics, formed between any two of the metal layersin order to prevent an interlayer short circuit from occurring. Inaddition, a pure metal or an alloy with low electric resistance issuitably used as the material for the metal layers. In general, forexamples of pure metals, Cr, Al, Cu, Mo, Ta, and W can be used. Asexamples of alloys with low electric resistance, an aluminum alloycontaining one or more selected from the other elements, such as Al—Cu,Al—Cu—Si, Al—Pd, and Al—Nd, is used. Preferably, pure aluminum isemployed as the material for metal layers. It is because aluminum hasconsiderable adhesion with the substrate, and considerable etchingcharacteristics in manufacturing as well as low electric resistivity.Besides, the earth contains much aluminum than other metal elements.Thus, aluminum is available and low in cost.

However, it still has disadvantages to use pure aluminum, which has amelting point lower than other metals, as the element for metal layers.Referring to FIG. 1A, it illustrates the deposition of a metal on aglass plate. In the manufacturing of thin film transistors, firstly,grains 104 are formed on a glass plate 102 by the deposition of metalunder relatively low temperature (about 150° C.) and grain boundaries106 are formed between the grains. In fact, the grains will not formedregularly in the same way as shown in FIG. 1A and the regular grainsshown in FIG. 1A are for the sake of illustration. Next, annealing isperformed so that the increased vibration of the grains by heating athigh temperature causes the re-arrangement of the atoms of the grains,thereby reducing defects of the grains and re-crystallizing the grains.After the re-crystallization, inner stress of the grains is rapidlyreduced by the reduction of the density of defects such as dislocation.If the annealing temperature is being increased and raises the grainsformed in the re-crystallization to a higher energy level exceeding thesurface energy among the grains, the grains begin to grow while thesmaller ones of them vanish. Consequently, the growth of the grainsyields larger grains and the grain boundaries of the smaller grainsvanish. Thus, the inner stress of the grains is further reduced to alower level.

When pure aluminum is used as the wiring layer material, hillock and thelike may be produced. FIG. 1B shows the hillock by illustrating theglass plate with pure aluminum as the wiring layer material afterannealing. In the annealing, the high temperature causes the thermalexpansion of Al grain 104 and glass plate 102. Since aluminum has agreater thermal expansion coefficient than the glass, a substantialcompressive stress by the Al grain 104 is applied to the glass plate102. By this compressive stress, the aluminum atoms move along grainboundary 106 to cause a hillock 110. The hillock and the like, such asthe hillock 110, may cause the unevenness of the thickness of the otherlayers in the subsequent fabrication process. Besides, in the worsecase, an interlayer short circuit may occur when a large hillockpenetrates an insulting layer (not shown) to be formed between theunderlying metal layer and the overlying metal layer, and touches theoverlying metal layer.

Hence, it is necessary to solve the problem of hillock in order to useAl as the wiring material. Conventionally, there are two approaches tothis problem. The first approach is to use the other element having ahigh melting point, such as Nd, Ti, Zr, Ta, Si, and Cu, as the wiringmaterial. FIG. 2A shows that grains 204 of an Al alloy formed on a glassplate 202 after annealing. As shown in FIG. 2A, there is no hillockformed among grain boundaries 206 of the grains 204 of the Al alloy.Since the atoms of the additional element of the Al alloy cannotdissolve in Al grains, as the grains 240 grow, the atoms of theadditional element move to the grain boundaries 206 and gradually formsmall particles 210 among the grain boundaries 206. Thus, when Al atomsmove along the grain boundaries 206, the small particles 210 hinder theAl atoms from moving above the grains 204, suppressing the formation ofhillock.

The second approach is to form a metal layer with high melting pointcovering the Al grains so as to suppress the growth of hillock. FIG. 2Billustrates a metal layer capping the Al grains. After a metal layer 212with a high melting point is plated over the Al grains 204, annealing isperformed. Since the metal layer 212 works as caps for covering theexits formed by the grain boundaries 206 among the Al grains 204, Alatoms are blocked from forming hillocks along the grain boundaries 206.In addition, there is provided with a variant of the second approachwhere an Al layer in an amorphous phase is substituted for the metallayer 212. And Al layer in an amorphous state can be formed on thegrains 204 for the suppression of the formation of hillock.

For these convention approaches to the problem of forming hillocks, itis the first one that is the most effective and usually employed. Forexample, a Japanese company, Kobelco, provides an Al—Nd alloy as thewiring material for metal layers, which is described in U.S. Pat. No.6,033,542 to Yamamoto, et al. Nd has a large atomic weight and a highmelting point, so that Nd can form small particles to hinder Al atomsfrom moving along the grain boundaries and forming hillocks. In thisway, hillocks do not occur even if the temperature reaches 300° C.However, manufacturing cost is increased because Nd is a rare earthelement, and it is required to apply a low sputtering rate in order toavoid splashing. Besides, Nd has a high resistivity so that an Al—Ndalloy has a resistivity higher than that of the pure aluminum.

As described above, the use of Al as wiring or electrode material ingeneral semiconductor and liquid crystal display manufacturing isdesired so that the study of the prevention of generating hillocks whenAl is used therein is of great significant.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a conductivelayerfor preventing hillocks and method of forming the same. By using abarrier aluminum (Al) layer as the buffering layer, which thermalexpansion coefficient of the barrier layer is between that of the pureAl layer and the substrate, the hillocks and the like are effectivelyprevented. Also, the resistance is low and the production cost isdecreased.

The invention achieves the objects by providing a conductive layer forpreventing hillocks comprising at least two aluminum (Al) layers formedon a substrate, wherein said at least two Al layers comprise: a barrierAl layer formed on the substrate, and a pure Al layer formed on thebarrier Al layer. In the conductive layer of the invention, resistivityof the barrier Al layer is larger than resistivity of the pure Al layer.The pure Al layer is at least 99.0 wt %, and preferably at least 99.9 wt%. Also, thermal expansion coefficient of the barrier Al layer issmaller than thermal expansion coefficient of the pure Al layer.

The barrier Al layer could at least contain one compound of aluminumnitride (AlNx), aluminum oxide (AlOx) and aluminum oxide-nitride(AlOxNy). If the thickness ratio of the barrier Al layer to the pure Allayer is in the range between about 1:6.25 and 1:1, the hillocks and thelike can be effectively inhibited. If the thickness ratio of the barrierAl layer to the pure Al layer is in the range between about 1:6.25 and1:2, a good sectional profile after etching the device is obtained. Thepure Al layer has a thickness ranged between about 1000 521 and 4500 Å.

Also, the barrier Al layer could be an Al—Nd alloy layer, wherein theAl—Nd alloy layer has a thickness ranged between about 100 Å and 4000 Å,and preferably in a thickness of about 300 Å and 90 Å. The pure Al layerhas a thickness ranged between about 500 Å and 4500 Å, and preferably ina thickness of about 1500 Å and 3000 Å, and the thickness ratio of theAl—Nd alloy layer to the pure Al layer is in the range between about1:6.67 and 1: 0.55.

Other objects, features, and advantages of the invention will becomeapparent from the following detailed description of the preferred butnon-limiting embodiments. The following description is made withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A (Prior Art) shows an example of the deposition of a metal on aglass plate;

FIG. 1B (Prior Art) shows an example of hillocks which occur in an Alwiring layer formed on a glass plate after annealing;

FIG. 2A (Prior Art) shows an example of grains of an Al alloy formed ona glass plate after annealing;

FIG. 2B (Prior Art) shows an example of a metal layer capping Al grainsformed on a glass plate;

FIG. 2C (Prior Art) shows an example of a barrier metal layer sandwichedbetween a glass plate and Al grains;

FIG. 3 shows a conductive layer with at least two aluminum layers on thesubstrate according to the embodiments of the present invention; and

FIG. 4 is a cross-sectional view of a bottom gate of TFT according tothe embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 shows a conductive layer with at least two aluminum layers on thesubstrate according to the embodiments of the present invention. Abarrier aluminum (Al) layer 304 is formed on the substrate 302, and apure Al layer 306 is then formed on the barrier Al layer 304, therebyinhibiting the occurrence of Al hillocks after undergoing the followingthermal processes.

In the first embodiment, the barrier Al layer at least contains onecompound of aluminum nitride (AlNx), aluminum oxide (AlOx) and aluminumoxide-nitride (AlOxNy). In the second embodiment, an aluminum-neodymium(Al—Nd) alloy is used as the material of the barrier Al layer for thespecific study. The related experimental results are also disclosedhereby.

First Embodiment

Please also refer to FIG. 3. In the first embodiment, a glass substrate304 is provided, and a barrier Al layer 304, such as an aluminum nitride(AlNx) layer, and aluminum oxide (AlOx) layer, an aluminum oxide-nitride(AlOxNy) layer, or any two or three layers combination thereof, isformed over the substrate 304. Then, a pure Al layer (at least 99.0 wt%, and preferably at least 99.9 wt %) 306 is formed over the barrier Allayer 304. According to the material of the barrier Al layer have beenchosen, the thermal expansion coefficient of the barrier Al layer 304 issmaller than that (thermal expansion coefficient) of the pure Al layer306, and larger than that of glass substrate 302. Therefore, theformation of Al hillocks can be successfully prevented after the deviceis exposed at a high temperature (or thermal shock) in the followingprocesses. Also, resistivity of the barrier Al layer 304 is higher thanthat of the pure Al layer 306.

As shown in Table 1, the thermal expansion coefficients andresistivities of pure Al, AlNx, AlOx, AlOxNy and three different glasssubstrates before annealing are listed. TABLE 1 Corning Asahi (glass NHT(glass (glass aluminum aluminum aluminum substrate) substrate)substrate) Aluminum nitride oxide oxide-nitride Sample 1737 E2000 NA35NA25 NA30 AN100 (Al) (AlN) (Al2O3) (AlOxNy) Thermal 37.8 32 37 26 32 38231 45 81 45˜81 Expansion Coefficient (×10⁻⁷/° C.) Resistivity NA NA NANA NA NA 2.65 × 10⁻⁶ 5.6 × 10¹³ 2 × 10¹³     2 × 10¹³ (Ωcm) ˜5.6 × 10¹³

During annealing (heating) process, the hillocks and the like will occurdue to the aluminum atoms moving along the grain boundaries by thethermal stress produced by a difference in thermal expansion coefficientbetween the glass substrate 302 and the pure Al layer 306. The featureof the present invention is to interpose a barrier Al layer 304 betweenthe glass substrate 302 and the pure Al layer 306, wherein the thermalexpansion coefficient of the barrier Al layer 304 is larger than thermalexpansion coefficient (that) of the glass substrate 302, but smallerthan that of the pure Al layer 306. Therefore, the barrier Al layer 304functions as a buffering layer for preventing the Al atoms migrationalong the grain boundaries to form the hillock and the like. Also, toobtain a considerably low resistivity (electric resistance) and a goodprofile of the device which has been gone through the post procedures(such as etching process), the pure Al layer 306 is physically thickerthan the barrier Al layer 304.

The experiments are conducted to investigate the conditions of thehillock-free device of the first embodiment of the present invention.First, a sputtering pure aluminum targets mounted in a vacuum chamber ofa sputtering apparatus. The aluminum nitride (AlNx) films were grown byreactive sputtering of an aluminum target in a nitrogen/argon (N2/Ar)gas mixture for different values of the deposition parameters: totalpressure, nitrogen content in the discharge gas, and substrate biasvoltage. Similarly, the aluminum oxide (AlOx) films were grown byreactive sputtering of an aluminum target in an oxygen/argon (O2/Ar) gasmixture, and the aluminum oxide-nitride (AlOxNy) films were grown in anitrogen/oxygen/argon (N2/O2/Ar) gas mixture.

Then, the stacked structure comprising two Al layers is heated(annealed) at a temperature of 34° C. for 30 minutes. Afterward, theuppermost layer of the stacked structure is observed by scanningelectron microscopy (SEM) after annealing process, to see if any hillockand the like occur and the sectional profile of the structure is good.The results are shown in Table 2. TABLE 2 Ratio of Sectional BarrierPure Al Barrier Al Occurrences profile of Al layer layer layer/ ofhillocks the thickness thickness Pure Al after stacked Example (Å) (Å)layer annealing structure 1 0 2000 0 Yes — 2 200 2000 1:10 Yes Not well3 300 2000 1:6.7 Yes Not well 4 400 2000 1:5 No good 5 500 2000 1:4 Nogood 6 600 2000 1:3.3 No good 7 1000 2000 1:2 No good 8 1500 2000 1:1.3No Not well 9 2000 2000 1:1 No Not well 10 250 1800 1:7.2 Yes Not well11 300 1800 1:6 No good 12 900 1800 1:2 No good 13 1800 1800 1:1 No Notwell 14 300 2500 1:8.3 Yes Not well 15 400 2500 1:6.25 No good 16 6002500 1:4.2 No good 17 700 2500 1:3.6 No good 18 1250 2500 1:2 No good 192500 2500 1:1 No Not well 20 600 4500 1:7.5 Yes Not well 21 750 4500 1:6No good 22 1500 4500 1:3 No good 23 2250 4500 1:2 No good 24 4500 45001:1 No Not well

EXAMPLE 1 Comparative Example

Under the sputtering conditions of film formation pressure of 0.3 Pa andAr gas, a pure Al film having a thickness of 2000 Å is formed on theglass substrate. Thereafter, the structure is annealed at a temperatureof 340° C. for 30 minutes. Then, it is observed by scanning electronmicroscopy (SEM) after annealing process.

The result shows that the hillocks and the like occur if no otherbuffering layer exists.

EXAMPLE 2

First, a barrier Al film which is made of the aluminum nitride having athickness of 200 Å is formed by reactive sputtering on the glasssubstrate under a film formation pressure of 0.5 Pa. A pure Al filmhaving a thickness of 2000 Å is formed on the barrier Al film under afilm formation pressure of 0.3 Pa. The thickness ratio of the barrier Allayer to the pure Al layer is about 1:10. Thus, the stacked structureincluding: pure Al layer (2000 Å)/AlNx (200 Å)/substrate, is annealed ata temperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results show that the hillocks and the like still occur. Thethickness ratio of the barrier Al layer to the pure Al layer (1:10) istoo low to buffer the thermal stress between the glass substrate and Alatoms. Also, after conducting the subsequent processes (such asphotolithography and etching), the barrier Al layers are over-etched andthe sectional profiles of these stacked structures are not well.

EXAMPLE 3

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer (AlNx) in a thickness of 300 Å on aglass substrate and a pure Al layer in a thickness of 2000 Å over thebarrier Al layer. The thickness ratio of the barrier Al layer to thepure Al layer is about 1:6.7.

The stacked structures are annealed at a temperature of 340° C. for 30minutes and then observed by SEM. The results indicate that hillocks andthe like are still raised. The thickness ratio of the barrier Al layerto the pure Al layer (1:6.7) is still too low to buffer the thermalstress between the glass substrate and Al atoms. Also, after conductingthe subsequent processes (such as photolithography and etching), thebarrier Al layers are over-etched and the sectional profiles of thesestacked structures are not well.

EXAMPLE 4

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 400 Å on a glasssubstrate and a pure Al layer in a thickness of 2000 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:5.

The stacked structures including: pure Al layer (2000 Å)/AlNx (400Å)/substrate is annealed at a temperature of 340° C. for 30 minutes andthen observed by SEM, respectively.

The results indicate that no hillocks and the like occur afterannealing. The thermal stress between the glass substrate and Al atomscan be effectively buffered if the thickness ratio of the barrier Allayer to the pure Al layer is 1:5. Also, after conducting the subsequentprocesses (such as photolithography and etching), the sectional profilesof these stacked structures are good.

EXAMPLE 5

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 500 Å on a glasssubstrate and a pure Al layer in a thickness of 2000 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:4.

These stacked structures are annealed at a temperature of 340° C. for 30minutes and then observed by SEM, respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 6

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 600 Å on a glasssubstrate and a pure Al layer in a thickness of 2000 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:3.3. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 7

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 1000 Å on a glasssubstrate and a pure Al layer in a thickness of 2000 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:2. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 8

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 1500 Å on a glasssubstrate and a pure Al layer in a thickness of 2000 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:1.3. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited. However, the sectional profiles of the structures are notwell. The pure Al layer is over-etched and the barrier Al layer isunder-etched, thereby leaving the barrier Al layer to excess.

EXAMPLE 9

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 2000 Å on a glasssubstrate and a pure Al layer in a thickness of 2000 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:1. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited. However, the sectional profiles of the structures are notwell. The pure Al layer is over-etched and the barrier Al layer isunder-etched, thereby leaving the barrier Al layer to excess.

EXAMPLE 10

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 250 Å on a glasssubstrate and a pure Al layer in a thickness of 1800 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:7.2. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that hillocks and the like are still raised. Thethickness ratio of the barrier Al layer to the pure Al layer (1:7.2) istoo low to buffer the thermal stress between the glass substrate and Alatoms. Also, the barrier Al layers are over-etched and the sectionalprofiles of these stacked structures are not well.

EXAMPLE 11

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 300 Å on a glasssubstrate and a pure Al layer in a thickness of 1800 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:6. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 12

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 900 Å on a glasssubstrate and a pure Al layer in a thickness of 1800 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:2. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 13

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 1800 Å on a glasssubstrate and a pure Al layer in a thickness of 1800 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:1. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited. However, the sectional profiles of the structures are notwell. The pure Al layer is over-etched and the barrier Al layer isunder-etched, thereby leaving the barrier Al layer to excess.

EXAMPLE 14

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 300 Å on a glasssubstrate and a pure Al layer in a thickness of 2500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:8.3. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that hillocks and the like are still raised. Thethickness ratio of the barrier Al layer to the pure Al layer (1:8.3) istoo low to buffer the thermal stress between the glass substrate and Alatoms. Also, the barrier Al layers are over-etched and the sectionalprofiles of these stacked structures are not well.

EXAMPLE 15

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 400 Å on a glasssubstrate and a pure Al layer in a thickness of 2500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:6.25. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 16

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 600 Å on a glasssubstrate and a pure Al layer in a thickness of 2500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:4.2. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 17

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 700 Å on a glasssubstrate and a pure Al layer in a thickness of 2500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:3.6. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 18

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 1250 Å on a glasssubstrate and a pure Al layer in a thickness of 2500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:2. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 19

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 2500 Å on a glasssubstrate and a pure Al layer in a thickness of 2500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:1. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited. However, the sectional profiles of the structures are notwell. The pure Al layer is over-etched and the barrier Al layer isunder-etched, thereby leaving the barrier Al layer to excess.

EXAMPLE 20

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 600 Å on a glasssubstrate and a pure Al layer in a thickness of 4500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:7.5. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that hillocks and the like are still raised. Thethickness ratio of the barrier Al layer to the pure Al layer (1:7.5) istoo low to buffer the thermal stress between the glass substrate and Alatoms. Also, the barrier Al layers are over-etched and the sectionalprofiles of these stacked structures are not well.

EXAMPLE 21

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 750 Å on a glasssubstrate and a pure Al layer in a thickness of 4500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:6.

These stacked structures are annealed at a temperature of 340° C. for 30minutes and then observed by SEM, respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 22

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 1500 Å on a glasssubstrate and a pure Al layer in a thickness of 4500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:3. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 23

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 2250 Å on a glasssubstrate and a pure Al layer in a thickness of 4500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:2.

These stacked structures are annealed at a temperature of 340° C. for 30minutes and then observed by SEM, respectively.

The results indicate that the hillocks and the like are effectivelyinhibited and the sectional profiles of the structures are good.

EXAMPLE 24

The procedures of Example 2 is followed to produced the stackedstructures having a barrier Al layer in a thickness of 4500 Å on a glasssubstrate and a pure Al layer in a thickness of 4500 Å over the barrierAl layer. The thickness ratio of the barrier Al layer to the pure Allayer is about 1:1. These stacked structures are annealed at atemperature of 340° C. for 30 minutes and then observed by SEM,respectively.

The results indicate that the hillocks and the like are effectivelyinhibited. However, the sectional profiles of the structures are notwell. The pure Al layer is over-etched and the barrier Al layer isunder-etched, thereby leaving the barrier Al layer to excess.

The results of Examples 1˜24 show that the hillock-free conductive layercomprises at least two aluminum (Al) layers formed on a substrate,including a barrier Al layer formed on the substrate and a pure Al layerformed on the barrier Al layer, wherein the pure Al layer has athickness ranged between about 1000 angstrom and 4500 angstrom, and thethickness ratio of the barrier Al layer to the pure Al layer is in therange between about 1:6.25 and 1:1. Therefore, the thermal stressproduced in accordance with the difference in the thermal expansionbetween the glass substrate and pure Al layer is effectively buffered.Also, in the first embodiment, materials used as the barrier Al layercould be aluminum nitride (AlNx), aluminum oxide (AlOx) and aluminumoxide-nitride (AlOxNy).

Moreover, the results of Examples listed in Table 2 show that thesectional profiles of these stacked structures are good if the pure Allayer has thickness ranged between about 1000 angstrom and 4500angstrom, and he barrier Al layer is physically thinner than the pure Allayer, and more particularly, the thickness ratio of the barrier Allayer to the pure Al layer is in the range between about 1:6.25 and 1:2.

Although there is only one pure Al layer is demonstrated above, it is tobe understood that the present invention is not restricted thereto. Theoccurrences of the hillocks and the like are still effectively preventedeven multiple (two, three, four, five, and so on) pure Al layers areformed above the barrier Al layer. In the practical application, thepure Al layer(s) could be substituted with the Al-based layer(s), suchas Al—Cu, Al—Cu—Si, Al—Pd, and Al—Cr, Al—Ti, and so on. Additionally,the barrier Al layer may contains multiple layers. For example, thebarrier Al layer could comprise a first AlNx layer, a second AlNx layerand a third AlNx layer which contain different amounts of nitrogen; orcould comprise a first AlOx layer, a second AlOx layer and a third AlOxlayer which contain different amounts of oxygen; or could comprise afirst AlOxNy layer, a second AlOxNy layer and a third AlOxNy layer whichcontain different ratio of oxygen to nitrogen. Also, the barrier Allayer could comprise multiple layers with different chemical compounds;for example, AlNx layer/AlOx layer, or AlNx layer/AlOxNy layer, or AlOxlayer/AlOxNy layer, or AlNx layer/AlOx layer/AlOxNy layer.

Second Embodiment

In the second embodiment, an aluminum-neodymium (Al—Nd) alloy layer isused as the barrier Al layer for preventing the occurrence of hillocksand the like. This stacked structure has often employed as the electrodepattern of thin film transistor (TFT).

Please also refer to FIG. 3. In the second embodiment, a glass substrate304 is provided, and an Al—Nd alloy layer (as the barrier Al layer 304)is formed over the substrate 304. The Al—Nd alloy layer has a thicknessranged between about 100 angstrom and 4000 angstrom, and preferably in athickness of about 300 angstrom and 900 angstrom.

Then, a pure Al layer 306 is formed over the Al—Nd alloy layer. The pureAl layer has a thickness ranged between about 500 angstrom and 4500angstrom, and preferably in a thickness of about 1500 angstrom and 3000angstrom.

The film formation condition of the Al—Nd alloy layer and the pure Allayer 306 are not in the limitation. The general film formationpressure, such as 0.3 Pa or 0.4 Pa, could be adapted. The Al—Nd alloylayer releases the stress produced during the thermal processes, so thatthe hillocks could be effectively inhibited.

Additionally, a protective layer (not shown in FIG. 3), for preventingthe oxidation of the Al layer, could be further formed over the pure Allayer 306. Metal such as molybdenum (Mo) and titanium (Ti), and compoundmolybdenum nitride (MoN) could be used as the material of the protectivelayer.

The experiments are conducted to investigate the conditions of thehillock-free device of the second embodiment of the present invention.Similarly, the stacked structure (comprising an Al—Nd alloy layer on thesubstrate and a pure Al layer on the Al—Nd alloy layer) is annealed at atemperature of 320° C. for 10 minutes. Afterward, the uppermost layer ofthe stacked structure is observed by scanning electron microscopy (SEM)after annealing process to see if any hillock and the like occur. Also,a Mo layer is further formed over the pure Al layer as a protectivelayer, and the sectional profile of the structure is observed by SEM.The results are shown in Table TABLE 3 Sectional Al-Nd alloy Ratio ofAl-Nd Occurrences of profile of layer Pure Al layer alloy layer tohillocks after the stacked Example thickness (Å) thickness (Å) Pure Allayer annealing structure 25 0 2000 0 Yes — 26 1800 0 — No good 27 3001000 1:3.3 No good 28 300 2000 1:6.7 No good 29 450 2000 1:4.4 No good30 450 1000 1:2.2 No good 31 900 2000 1:2.2 No good 32 900 1000 1:1.1 Nogood 33 1800 2000 1:1.1 No good 34 1800 1000 1:0.55 No good

EXAMPLE 25 Comparative Example

Under the sputtering conditions of film formation pressure of 0.3 Pa, apure Al film having a thickness of 2000 Å is formed on the substrate.Thereafter, the structure is annealed at a temperature of 320° C. for 10minutes. Then, it is observed by scanning electron microscopy (SEM)after annealing process.

The result shows that the hillocks and the like occur if only pure Allayer is employed.

EXAMPLE 26 Comparative Example

Under the sputtering conditions of film formation pressure of 0.3 Pa, anAl—Nd alloy film having a thickness of 1800 Å is formed on thesubstrate. Thereafter, the structure is annealed at a temperature of320° C. for 10 minutes. Then, it is observed by scanning electronmicroscopy (SEM) after annealing process.

The result shows that no hillocks occur if only Al—Nd alloy layer isused as the conductive layer.

Also, a metallic Mo layer is further formed on the Al—Nd alloy layer ina thickness of 1000 Å. Under SEM, it shows that the structure has a goodsectional profile.

However, material of Al—Nd alloy is expansive, it is less beneficial touse the Al—Nd alloy as the only material of the conductive layer. Also,the electric resistance for Al—Nd alloy is too high (about twice thevalue for Al), and more film formation time is needed for forming thethicker film in order to meet the electric requirement of the device.

EXAMPLE 27

Under the sputtering conditions of film formation pressure of 0.3 Pa, anAl—Nd alloy film having a thickness of 300 Å is formed on the substrate,and then a pure Al layer having a thickness of 1000 Å is formed on theAl—Nd alloy film. Thereafter, the structure is annealed at a temperatureof 320° C. for 10 minutes. Then, it is observed by scanning electronmicroscopy (SEM) after annealing process. The result shows no occurrenceof hillocks and the like.

Also, a metallic Mo layer is further formed on the pure Al layer in athickness of 900 Å. Under SEM, it shows that the structure has a goodsectional profile.

EXAMPLE 28

An Al—Nd alloy film having a thickness of 300 Å is formed on thesubstrate (film formation pressure of 0.3 Pa), and then a pure Al layerhaving a thickness of 2000 Å is formed on the Al—Nd alloy film.Thereafter, the structure is annealed at a temperature of 320° C. for 10minutes. Then, it is observed by scanning electron microscopy (SEM)after annealing process. The result also shows no occurrence of hillocksand the like.

A metallic Mo layer is further formed on the pure Al layer in athickness of 900 Å. Under SEM, it shows that the structure has a goodsectional profile.

EXAMPLE 29

An Al—Nd alloy film having a thickness of 450 Å is formed on thesubstrate (film formation pressure of 0.3 Pa), and then a pure Al layerhaving a thickness of 2000 Å is formed on the Al—Nd alloy film.Thereafter, the structure is annealed at a temperature of 320° C. for 10minutes. Then, it is observed by scanning electron microscopy (SEM)after annealing process. The result also shows no occurrence of hillocksand the like.

A metallic Mo layer is further formed on the pure Al layer in athickness of 900 Å. Under SEM, it shows that the structure has a goodsectional profile.

EXAMPLE 30

An Al—Nd alloy film having a thickness of 450 Å is formed on thesubstrate (film formation pressure of 0.3 Pa), and then a pure Al layerhaving a thickness of 1000 Å is formed on the Al—Nd alloy film. Thestructure is annealed at a temperature of 320° C. for 10 minutes, andthen observed by scanning electron microscopy (SEM). The result alsoshows no occurrence of hillocks and the like.

A metallic Mo layer is further formed on the pure Al layer in athickness of 900 Å. Under SEM, it shows that the structure has a goodsectional profile.

EXAMPLE 31

An Al—Nd alloy film having a thickness of 900 Å is formed on thesubstrate, and then a pure Al layer having a thickness of 2000 Å isformed on the Al—Nd alloy film. The structure is annealed at atemperature of 320° C. for 10 minutes, and then observed by scanningelectron microscopy (SEM). The result also shows no occurrence ofhillocks and the like.

A metallic Mo layer is further formed on the pure Al layer in athickness of 900 Å. Under SEM, it shows that the structure has a goodsectional profile.

EXAMPLE 32

An Al—Nd alloy film having a thickness of 900 Å is formed on thesubstrate, and then a pure Al layer having a thickness of 1000 Å isformed on the Al—Nd alloy film. The structure is annealed at atemperature of 320° C. for 10 minutes, and then observed by scanningelectron microscopy (SEM). The result also shows no occurrence ofhillocks and the like.

A metallic Mo layer is further formed on the pure Al layer in athickness of 900 Å. Under SEM, it shows that the structure has a goodsectional profile.

EXAMPLE 33

An Al—Nd alloy film having a thickness of 1800 Å is formed on thesubstrate, and then a pure Al layer having a thickness of 2000 Å isformed on the Al—Nd alloy film. The structure is annealed at atemperature of 320° C. for 10 minutes, and then observed by scanningelectron microscopy (SEM). The result also shows no occurrence ofhillocks and the like.

A metallic Mo layer is further formed on the pure Al layer in athickness of 900 Å. Under SEM, it shows that the structure has a goodsectional profile.

EXAMPLE 34

An Al—Nd alloy film having a thickness of 1800 Å is formed on thesubstrate, and then a pure Al layer having a thickness of 1000 Å isformed on the Al—Nd alloy film. The thickness ratio of the Al—Nd alloylayer to the pure Al layer is about 1:0.55. The structure is annealed ata temperature of 320° C. for 10 minutes, and then observed by scanningelectron microscopy (SEM). The result also shows no occurrence ofhillocks and the like.

A metallic Mo layer is further formed on the pure Al layer in athickness of 900 Å. Under SEM, it shows that the structure has a goodsectional profile.

It is noted that the pure Al layer is generally thicker than the Al—Ndalloy (barrier layer) in the second embodiment (Examples 27-33);however, the pure Al layer can be thinner than the Al—Nd alloy layer(Example 34) for effectively preventing hillocks and the like.

According to the results of Examples 27˜34, an Al—Nd alloy layerinterposed between the substrate and the pure Al layer does effectivelyprevent the occurrence of hillocks and the like.

The results of Examples 27˜34 show that the conductive layer comprisesat least two aluminum (Al) layers formed on a substrate, including abarrier Al (Al—Nd alloy) layer formed on the substrate and a pure Allayer formed on the barrier Al layer, wherein the barrier Al layer has athickness ranged between about 300 angstrom and 1800 angstrom, the pureAl layer has a thickness ranged between about 1000 angstrom and 2000angstrom.

The thickness ratio of the barrier Al layer to the pure Al layer is inthe range between about 1:6.67 and 1:0.55. Therefore, the thermal stressproduced in accordance with the difference in the thermal expansionbetween the glass substrate and pure Al layer is effectively buffered.Accordingly, for preventing the occurrence of hillocks and keeping goodsectional profiles of these stacked structures, the Al—Nd alloy layerhas a thickness ranged between about 100 angstrom and 4000 angstrom, andpreferably in a range of about 300 angstrom and 900 angstrom. The pureAl layer has a thickness ranged between about 500 angstrom and 4500angstrom, and preferably in a range of about 1500 angstrom and 3000angstrom.

In the practical application, most of the stacked structure (Examples27-33) according to the second embodiment of the invention couldcomprise a very thick pure Al layer and a very thin Al—Nd alloy layer inthe consideration of production cost. For example, the cost for thestructure comprising 450 Å Al—Nd alloy layer and 2000 Å pure Al layer is66% of the cost for the structure only comprising 1800 Å Al—Nd alloylayer. Moreover, the electric resistance of Al is lower than that ofAl—Nd alloy (about 50%). Thus, the device requirement can be satisfiedby using the thinner complex film of AlNd/Al, thereby decreasing thesize and improving the evenness of the device.

The structure according to the embodiments of the invention can be usedas a conduct pattern such as a wiring pattern or an electrode pattern ofan electronic device. In the following description, the structure of theinvention is used as the metallic gate electrode of a thin filmtransistor (TFT).

FIG. 4 is a cross-sectional view of a bottom gate of TFT according tothe embodiments of the invention. First, a substrate 400 is provided. Aconductive layer is deposited over the substrate 400, and etched to forma gate electrode 410.

According to the first embodiment of the invention, the gate electrode410 comprises at least two Al layers, including a barrier Al layer onthe substrate 400 and a pure Al layer on the barrier Al layer. Thebarrier Al layer at least contains one compound of aluminum nitride(AlNx), aluminum oxide (AlOx) and aluminum oxide-nitride (AlOxNy). Thethickness ratio of the barrier Al layer to the pure Al layer is in therange between about 1:6.25 and 1: 2, in order to obtain a good sectionalprofile after the device is etched. Also, a Mo layer, or a MoN layer canbe further formed on the pure Al layer, in a thickness ranged from 300 Åto 1200 Å, for the purpose of protection.

According to the second embodiment of the invention, the gate electrode410 comprises at least two Al layers, including an Al—Nd alloy layer onthe substrate 400 and a pure Al layer on the Al—Nd alloy layer. TheAl—Nd alloy layer has a thickness ranged between about 100 Å and 4000 Å,and preferably in a thickness of about 300 Å and 900 Å. The pure Allayer has a thickness ranged between about 500 Å and 4500 Å, andpreferably in a thickness of about 1500 Å and 3000 Å. The thicknessratio of the barrier Al layer to the pure Al layer is in the rangebetween about 1:6.67 and 1:0.55. Similarly, a Mo layer, or a MoN layercan be further formed on the pure Al layer, in a thickness ranged from300 Å to 1200 Å, for the purpose of protection.

Afterward, a gate insulating layer 420 is formed over the gate electrode410. By deposition and photolithography, an amorphous silicon layer 430and an ohmic contact layer 440 are then formed on the gate insulatinglayer 420.

Next, a source region 460 and a drain region 465 are formed bydepositing and patterning a metal (such as Cr and Al) layer over thesubstrate 400. Also, a channel region is also formed to expose thesurface of the amorphous silicon layer 430, wherein the source region460 and the drain region 465 are divided by the channel.

Afterward, a passivation layer 470 is formed over the substrate 400 forcovering the source region 460, the drain region 465 and the channel. Byphotolithography and etching, an opening is formed in the passivationlayer 470 to expose the drain region 460. Finally, a patternedtransparent electrode (ITO) 380 is formed over the passivation layer470, and the opening is also filled with the transparent electrode.

It is, of course, understood that the invention could be applied invaried electronic devices, not limited in the application of TFT device.According to the stacked structure of the invention, the production costcan be considerably reduced, and hillocks and the like can beeffectively inhibited. Also, the electric resistance of the Al layercombination (a barrier layer under a pure Al layer) is much lower thanthat of only one Al-based layer (such as an Al—Nd alloy layer), therebyimproving the electric characteristics of the applied device.

While the invention has been described by way of examples and in termsof the preferred embodiments, it is to be understood that the inventionis not limited thereto. On the contrary, it is intended to cover variousmodifications and similar arrangements and procedures, and the scope ofthe appended claims therefore should be accorded the broadestinterpretation so as to encompass all such modifications and similararrangements and procedures.

1. A conductive layer comprising at least two aluminum (Al) layersformed on a substrate, wherein said at least two Al layers comprise: abarrier Al layer formed on the substrate; and a pure Al layer formed onthe barrier Al layer.
 2. The conductive layer according to claim 1,wherein resistivity of the barrier Al layer is larger than resistivityof the pure Al layer.
 3. The conductive layer according to claim 1,wherein aluminum of the pure Al layer is at least about 99.0 wt %. 4.The conductive layer according to claim 1, wherein aluminum of the pureAl layer is at least about 99.9 wt %.
 5. The conductive layer accordingto claim 1, wherein thermal expansion coefficient of the barrier Allayer is smaller than thermal expansion coefficient of the pure Allayer.
 6. The conductive layer according to claim 5, wherein the barrierAl layer at least contains one compound of aluminum nitride (AlNx),aluminum oxide (AlOx) and aluminum oxide-nitride (AlOxNy).
 7. Theconductive layer according to claim 5, wherein the pure Al layer has athickness ranged between about 1000 angstrom and 4500 angstrom, and thethickness ratio of the barrier Al layer to the pure Al layer is in therange between about 1:6.25 and 1:1.
 8. The conductive layer according toclaim 1, wherein the barrier Al layer is an aluminum-neodymium (Al—Nd)alloy layer.
 9. The conductive layer according to claim 8, wherein thepure Al layer is physically thicker than the barrier Al layer.
 10. Theconductive layer according to claim 8, wherein the Al—Nd alloy layer hasa thickness ranged between about 100 angstrom and 4000 angstrom, and thepure Al layer has a thickness ranged between about 500 angstrom and 4500angstrom.
 11. The conductive layer according to claim 8, wherein theAl—Nd alloy layer is preferably in a thickness of about 300 angstrom and900 angstrom, and the pure Al layer is preferably in a thickness ofabout 1500 angstrom and 3000 angstrom.
 12. The conductive layeraccording to claim 8, wherein the thickness ratio of the Al—Nd alloylayer to the pure Al layer is in the range between about 1:6.67 and1:0.55.
 13. An electronic device, at least comprising a conductivepattern formed on a substrate, wherein said the conductive patterncomprise: a barrier Al layer formed on the substrate; and a pure Allayer formed on the barrier Al layer.
 14. The electronic deviceaccording to claim 13, wherein resistivity of the barrier Al layer islarger than resistivity of the pure Al layer.
 15. The electronic deviceaccording to claim 13, wherein aluminum of the pure Al layer is at leastabout 99.0 wt %.
 16. The electronic device according to claim 13,wherein aluminum of the pure Al layer is at least about 99.9 wt %. 17.The electronic device according to claim 13, wherein thermal expansioncoefficient of the barrier Al layer is smaller than thermal expansioncoefficient of the pure Al layer.
 18. The electronic device according toclaim 17, wherein the barrier Al layer at least contains one compound ofaluminum nitride (AlNx), aluminum oxide (AlOx) and aluminumoxide-nitride (AlOxNy).
 19. The electronic device according to claim 17,wherein the pure Al layer has a thickness ranged between about 1000angstrom and 4500 angstrom, and the thickness ratio of the barrier Allayer to the pure Al layer is in the range between about 1:6.25 and 1:2.20. The electronic device according to claim 13, wherein the pure Allayer is physically thicker than the barrier Al layer.
 21. Theelectronic device according to claim 13, wherein the barrier Al layer isan aluminum-neodymium (Al—Nd) alloy layer.
 22. The electronic deviceaccording to claim 21, wherein the Al—Nd alloy layer has a thicknessranged between about 100 angstrom and 4000 angstrom, and the pure Allayer has a thickness ranged between about 500 angstrom and 4500angstrom.
 23. The electronic device according to claim 21, wherein theAl—Nd alloy layer is preferably in a thickness of about 300 angstrom and900 angstrom, and the pure Al layer is preferably in a thickness ofabout 1500 angstrom and 3000 angstrom.
 24. The electronic deviceaccording to claim 21, wherein the thickness ratio of the Al—Nd alloylayer to the pure Al layer is in the range between about 1:6.67 and1:0.55.
 25. The electronic device according to claim 13, wherein theconductive pattern comprising a gate wiring pattern.
 26. The electronicdevice according to claim 13, wherein the electronic device is a thinfilm transistor (TFT) device.
 27. The electronic device according toclaim 26, wherein a protective layer is further formed on the electrodepattern.
 28. The electronic device according to claim 27, wherein theprotective layer is made of material selected from molybdenum (Mo),molybdenum nitride (MoN), titanium (Ti), or alloy of the combination.29. An electronic device, at least comprising a patterned electrode,wherein said the patterned electrode comprise: an aluminum-neodymium(Al—Nd) alloy layer; and a pure Al layer formed on the Al—Nd alloylayer.
 30. The electron device according to claim 29, wherein aluminumof the pure Al layer is at least about 99.0 wt %.
 31. The electronicdevice according to claim 29, wherein aluminum of the pure Al layer isat least about 99.9 wt %.
 32. The electronic device according to claim29, wherein the thickness ratio of the Al—Nd alloy layer to the pure Allayer is in the range between about 1:6.67 and 1:0.55.
 33. Theelectronic device according to claim 29, wherein the Al—Nd alloy layerhas a thickness ranged between about 100 angstrom and 4000 angstrom, andthe pure Al layer has a thickness ranged between about 500 angstrom and4500 angstrom.
 34. The electronic device according to claim 29, whereinthe Al—Nd alloy layer is preferably in a thickness of about 300 angstromand 900 angstrom, and the pure Al layer is preferably in a thickness ofabout 1500 angstrom and 3000 angstrom.
 35. The electronic deviceaccording to claim 29, wherein a protective layer is further formed onthe pure Al layer.
 36. The electronic device according to claim 35,wherein the protective layer is made of material selected frommolybdenum (Mo), molybdenum nitride (MoN), titanium (Ti), or alloy ofthe combination.
 37. In a thin film transistor (TFT) device, having asubstrate, a gate electrode layer formed on the substrate, above thegate electrode layer having a gate insulating layer, an amorphoussilicon layer and an ohmic contact layer, wherein a channel region abovethe gate electrode layer is formed between a source region and a drainregion, which the source region and the drain region covering the ohmiccontact layer and part of the substrate are covered by a protectinglayer, the improvement which comprises:the gate electrode layercomprising a barrier aluminum (Al) layer and a pure Al layer formed onthe barrier Al layer.
 38. The TFT device according to claim 37, whereinresistivity of the barrier Al layer is larger than resistivity of thepure Al layer.
 39. The TFT device according to claim 37, whereinaluminum of the pure Al layer is at least about 99.0 wt %.
 40. The TFTdevice according to claim 37, wherein aluminum of the pure Al layer isat least about 99.9 wt %.
 41. The TFT device according to claim 37,wherein thermal expansion coefficient of the barrier Al layer is smallerthan thermal expansion coefficient of the pure Al layer, but larger thanthermal expansion coefficient of the substrate.
 42. The TFT deviceaccording to claim 41, wherein the barrier Al layer at least containsone compound of aluminum nitride (AlNx), aluminum oxide (AlOx) andaluminum oxide-nitride (AlOxNy).
 43. The TFT device according to claim42, wherein the thickness ratio of the barrier Al layer to the pure Allayer is in the range between about 1:6.25 and 1:1.
 44. The TFT deviceaccording to claim 37, wherein the barrier Al layer is analuminum-neodymium (Al—Nd) alloy layer.
 45. The TFT device according toclaim 44, wherein the Al—Nd alloy layer has a thickness ranged betweenabout 100 angstrom and 4000 angstrom, and the pure Al layer has athickness ranged between about 500 angstrom and 4500 angstrom.
 46. TheTFT device according to claim 44, wherein the thickness ratio of theAl—Nd alloy layer to the pure Al layer is in the range between about 1:6.67 and 1:0.55.
 47. The TFT device according to claim 44, wherein aprotective layer is further formed on the pure Al layer.
 48. The TFTdevice according to claim 47, wherein the protective layer is made ofmaterial selected from molybdenum (Mo), molybdenum nitride (MoN),titanium (Ti), or alloy of the combination.
 49. A method of forming aconductive layer for preventing the formation of the Al hillocks,wherein the conductive layer is formed on a substrate and at leastcomprises two Al layers, the method comprising the steps of: forming abarrier Al layer on the substrate; and forming a pure Al layer on thebarrier Al layer.
 50. The method according to claim 49, whereinresistivity of the barrier Al layer is larger than resistivity of thepure Al layer.
 51. The method according to claim 49, wherein aluminum ofthe pure Al layer is at least about 99.0 wt %.
 52. The method accordingto claim 49, wherein aluminum of the pure Al layer is at least about99.9 wt %.
 53. The method according to claim 49, wherein thermalexpansion coefficient of the barrier Al layer is smaller than thermalexpansion coefficient of the pure Al layer.
 54. The method according toclaim 53, wherein the barrier Al layer at least contains one compound ofaluminum nitride (AlNx), aluminum oxide (AlOx) and aluminumoxide-nitride (AlOxNy).
 55. The method according to claim 54, whereinthe pure Al layer has a thickness ranged between about 1000 angstrom and4500 angstrom, and the thickness ratio of the barrier Al layer to thepure Al layer is in the range between about 1:6.25 and 1:1.
 56. Themethod according to claim 49, wherein the barrier Al layer is analuminum-neodymium (Al—Nd) alloy layer.
 57. The method according toclaim 56, wherein the pure Al layer is physically thicker than the Al—Ndalloy layer.
 58. The method according to claim 56, wherein the Al—Ndalloy layer has a thickness ranged between about 100 angstrom and 4000angstrom, and the pure Al layer has a thickness ranged between about 500angstrom and 4500 angstrom.
 59. The method according to claim 56,wherein the Al—Nd alloy layer is preferably in a thickness of about 300angstrom and 900 angstrom, and the pure Al layer is preferably in athickness of about 1500 angstrom and 3000 angstrom.
 60. The methodaccording to claim 56, wherein the thickness ratio of the Al—Nd alloylayer to the pure Al layer is in the range between about 1:6.67 and1:0.55.
 61. The method according to claim 56, wherein the Al—Nd alloylayer and the pure Al layer are formed under a film formation pressureof about 0.3 Pa.